From: Matthew Dempsky <mdempsky@google.com>
Date: Sat, 14 Nov 2020 04:38:21 +0000 (-0800)
Subject: [dev.regabi] cmd/compile: replace CTNIL with ONIL
X-Git-Tag: go1.17beta1~1539^2~471
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=88a9e2f9ad0ad3ef1e254e9150f4649e57b0a296;p=gostls13.git

[dev.regabi] cmd/compile: replace CTNIL with ONIL

Properly speaking, "nil" is a zero value, not a constant. So
go/constant does not have a representation for it. To allow replacing
Val with constant.Value, we split out ONIL separately from OLITERAL so
we can get rid of CTNIL.

Passes toolstash-check.

Change-Id: I4c8e60cae3b3c91bbac43b3b0cf2a4ade028d6cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/272650
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
---

diff --git a/src/cmd/compile/internal/gc/const.go b/src/cmd/compile/internal/gc/const.go
index b92c8d66b5..42ac3a26f8 100644
--- a/src/cmd/compile/internal/gc/const.go
+++ b/src/cmd/compile/internal/gc/const.go
@@ -24,7 +24,6 @@ const (
 	CTCPLX
 	CTSTR
 	CTBOOL
-	CTNIL
 )
 
 type Val struct {
@@ -34,7 +33,6 @@ type Val struct {
 	// *Mpflt   float when Ctype() == CTFLT
 	// *Mpcplx  pair of floats when Ctype() == CTCPLX
 	// string   string when Ctype() == CTSTR
-	// *Nilval  when Ctype() == CTNIL
 	U interface{}
 }
 
@@ -45,8 +43,6 @@ func (v Val) Ctype() Ctype {
 		panic("unreachable")
 	case nil:
 		return CTxxx
-	case *NilVal:
-		return CTNIL
 	case bool:
 		return CTBOOL
 	case *Mpint:
@@ -71,8 +67,6 @@ func eqval(a, b Val) bool {
 	default:
 		Fatalf("unexpected Ctype for %T", a.U)
 		panic("unreachable")
-	case *NilVal:
-		return true
 	case bool:
 		y := b.U.(bool)
 		return x == y
@@ -99,8 +93,6 @@ func (v Val) Interface() interface{} {
 	default:
 		Fatalf("unexpected Interface for %T", v.U)
 		panic("unreachable")
-	case *NilVal:
-		return nil
 	case bool, string:
 		return x
 	case *Mpint:
@@ -112,8 +104,6 @@ func (v Val) Interface() interface{} {
 	}
 }
 
-type NilVal struct{}
-
 // Int64Val returns n as an int64.
 // n must be an integer or rune constant.
 func (n *Node) Int64Val() int64 {
@@ -245,7 +235,7 @@ func convlit1(n *Node, t *types.Type, explicit bool, context func() string) *Nod
 		return n
 	}
 
-	if n.Op == OLITERAL {
+	if n.Op == OLITERAL || n.Op == ONIL {
 		// Can't always set n.Type directly on OLITERAL nodes.
 		// See discussion on CL 20813.
 		n = n.rawcopy()
@@ -253,6 +243,9 @@ func convlit1(n *Node, t *types.Type, explicit bool, context func() string) *Nod
 
 	// Nil is technically not a constant, so handle it specially.
 	if n.Type.Etype == TNIL {
+		if n.Op != ONIL {
+			Fatalf("unexpected op: %v (%v)", n, n.Op)
+		}
 		if t == nil {
 			yyerror("use of untyped nil")
 			n.SetDiag(true)
@@ -1039,8 +1032,6 @@ func idealType(ct Ctype) *types.Type {
 		return types.UntypedFloat
 	case CTCPLX:
 		return types.UntypedComplex
-	case CTNIL:
-		return types.Types[TNIL]
 	}
 	Fatalf("unexpected Ctype: %v", ct)
 	return nil
@@ -1189,7 +1180,7 @@ func indexconst(n *Node) int64 {
 // Expressions derived from nil, like string([]byte(nil)), while they
 // may be known at compile time, are not Go language constants.
 func (n *Node) isGoConst() bool {
-	return n.Op == OLITERAL && n.Val().Ctype() != CTNIL
+	return n.Op == OLITERAL
 }
 
 func hascallchan(n *Node) bool {
diff --git a/src/cmd/compile/internal/gc/esc.go b/src/cmd/compile/internal/gc/esc.go
index 6f328ab5ea..b7d1dfc92a 100644
--- a/src/cmd/compile/internal/gc/esc.go
+++ b/src/cmd/compile/internal/gc/esc.go
@@ -152,7 +152,7 @@ func mayAffectMemory(n *Node) bool {
 	// We're ignoring things like division by zero, index out of range,
 	// and nil pointer dereference here.
 	switch n.Op {
-	case ONAME, OCLOSUREVAR, OLITERAL:
+	case ONAME, OCLOSUREVAR, OLITERAL, ONIL:
 		return false
 
 	// Left+Right group.
diff --git a/src/cmd/compile/internal/gc/escape.go b/src/cmd/compile/internal/gc/escape.go
index 757b4652ca..bc0eb98d76 100644
--- a/src/cmd/compile/internal/gc/escape.go
+++ b/src/cmd/compile/internal/gc/escape.go
@@ -476,7 +476,7 @@ func (e *Escape) exprSkipInit(k EscHole, n *Node) {
 	default:
 		Fatalf("unexpected expr: %v", n)
 
-	case OLITERAL, OGETG, OCLOSUREVAR, OTYPE:
+	case OLITERAL, ONIL, OGETG, OCLOSUREVAR, OTYPE:
 		// nop
 
 	case ONAME:
diff --git a/src/cmd/compile/internal/gc/fmt.go b/src/cmd/compile/internal/gc/fmt.go
index f61ea8aaac..9b57d131b1 100644
--- a/src/cmd/compile/internal/gc/fmt.go
+++ b/src/cmd/compile/internal/gc/fmt.go
@@ -571,9 +571,6 @@ func (v Val) vconv(s fmt.State, flag FmtFlag) {
 	case bool:
 		fmt.Fprint(s, u)
 
-	case *NilVal:
-		fmt.Fprint(s, "nil")
-
 	default:
 		fmt.Fprintf(s, "<ctype=%d>", v.Ctype())
 	}
@@ -1207,6 +1204,7 @@ var opprec = []int{
 	OMAPLIT:        8,
 	ONAME:          8,
 	ONEW:           8,
+	ONIL:           8,
 	ONONAME:        8,
 	OOFFSETOF:      8,
 	OPACK:          8,
@@ -1323,6 +1321,9 @@ func (n *Node) exprfmt(s fmt.State, prec int, mode fmtMode) {
 	case OPAREN:
 		mode.Fprintf(s, "(%v)", n.Left)
 
+	case ONIL:
+		fmt.Fprint(s, "nil")
+
 	case OLITERAL: // this is a bit of a mess
 		if mode == FErr {
 			if n.Orig != nil && n.Orig != n {
@@ -1334,10 +1335,7 @@ func (n *Node) exprfmt(s fmt.State, prec int, mode fmtMode) {
 				return
 			}
 		}
-		if n.Val().Ctype() == CTNIL && n.Orig != nil && n.Orig != n {
-			n.Orig.exprfmt(s, prec, mode)
-			return
-		}
+
 		if n.Type != nil && !n.Type.IsUntyped() {
 			// Need parens when type begins with what might
 			// be misinterpreted as a unary operator: * or <-.
diff --git a/src/cmd/compile/internal/gc/iexport.go b/src/cmd/compile/internal/gc/iexport.go
index 47910eb3b9..b48a840d00 100644
--- a/src/cmd/compile/internal/gc/iexport.go
+++ b/src/cmd/compile/internal/gc/iexport.go
@@ -759,8 +759,6 @@ func constTypeOf(typ *types.Type) Ctype {
 	}
 
 	switch typ.Etype {
-	case TCHAN, TFUNC, TMAP, TNIL, TINTER, TPTR, TSLICE, TUNSAFEPTR:
-		return CTNIL
 	case TBOOL:
 		return CTBOOL
 	case TSTRING:
@@ -790,9 +788,6 @@ func (w *exportWriter) value(typ *types.Type, v Val) {
 	// and provides a useful consistency check.
 
 	switch constTypeOf(typ) {
-	case CTNIL:
-		// Only one value; nothing to encode.
-		_ = v.U.(*NilVal)
 	case CTBOOL:
 		w.bool(v.U.(bool))
 	case CTSTR:
@@ -1207,11 +1202,19 @@ func (w *exportWriter) expr(n *Node) {
 	switch op := n.Op; op {
 	// expressions
 	// (somewhat closely following the structure of exprfmt in fmt.go)
-	case OLITERAL:
-		if n.Val().Ctype() == CTNIL && n.Orig != nil && n.Orig != n {
+	case ONIL:
+		if !n.Type.HasNil() {
+			Fatalf("unexpected type for nil: %v", n.Type)
+		}
+		if n.Orig != nil && n.Orig != n {
 			w.expr(n.Orig)
 			break
 		}
+		w.op(OLITERAL)
+		w.pos(n.Pos)
+		w.typ(n.Type)
+
+	case OLITERAL:
 		w.op(OLITERAL)
 		w.pos(n.Pos)
 		w.value(n.Type, n.Val())
diff --git a/src/cmd/compile/internal/gc/iimport.go b/src/cmd/compile/internal/gc/iimport.go
index df193cd8e1..ac565a6632 100644
--- a/src/cmd/compile/internal/gc/iimport.go
+++ b/src/cmd/compile/internal/gc/iimport.go
@@ -293,7 +293,8 @@ func (r *importReader) doDecl(n *Node) {
 		importalias(r.p.ipkg, pos, n.Sym, typ)
 
 	case 'C':
-		typ, val := r.value()
+		typ := r.typ()
+		val := r.value(typ)
 
 		importconst(r.p.ipkg, pos, n.Sym, typ, val)
 
@@ -354,12 +355,8 @@ func (r *importReader) doDecl(n *Node) {
 	}
 }
 
-func (p *importReader) value() (typ *types.Type, v Val) {
-	typ = p.typ()
-
+func (p *importReader) value(typ *types.Type) (v Val) {
 	switch constTypeOf(typ) {
-	case CTNIL:
-		v.U = &NilVal{}
 	case CTBOOL:
 		v.U = p.bool()
 	case CTSTR:
@@ -810,11 +807,20 @@ func (r *importReader) node() *Node {
 	// case OPAREN:
 	// 	unreachable - unpacked by exporter
 
+	// case ONIL:
+	//	unreachable - mapped to OLITERAL
+
 	case OLITERAL:
 		pos := r.pos()
-		typ, val := r.value()
+		typ := r.typ()
 
-		n := npos(pos, nodlit(val))
+		var n *Node
+		if typ.HasNil() {
+			n = nodnil()
+		} else {
+			n = nodlit(r.value(typ))
+		}
+		n = npos(pos, n)
 		n.Type = typ
 		return n
 
diff --git a/src/cmd/compile/internal/gc/inl.go b/src/cmd/compile/internal/gc/inl.go
index 4aa561da6e..a882e91dce 100644
--- a/src/cmd/compile/internal/gc/inl.go
+++ b/src/cmd/compile/internal/gc/inl.go
@@ -459,7 +459,7 @@ func inlcopy(n *Node) *Node {
 	}
 
 	switch n.Op {
-	case ONAME, OTYPE, OLITERAL:
+	case ONAME, OTYPE, OLITERAL, ONIL:
 		return n
 	}
 
@@ -1322,7 +1322,7 @@ func (subst *inlsubst) node(n *Node) *Node {
 		}
 		return n
 
-	case OLITERAL, OTYPE:
+	case OLITERAL, ONIL, OTYPE:
 		// If n is a named constant or type, we can continue
 		// using it in the inline copy. Otherwise, make a copy
 		// so we can update the line number.
diff --git a/src/cmd/compile/internal/gc/obj.go b/src/cmd/compile/internal/gc/obj.go
index 8fe480b65f..77f9afb44d 100644
--- a/src/cmd/compile/internal/gc/obj.go
+++ b/src/cmd/compile/internal/gc/obj.go
@@ -591,12 +591,15 @@ func litsym(n, c *Node, wid int) {
 	if n.Op != ONAME {
 		Fatalf("litsym n op %v", n.Op)
 	}
-	if c.Op != OLITERAL {
-		Fatalf("litsym c op %v", c.Op)
-	}
 	if n.Sym == nil {
 		Fatalf("litsym nil n sym")
 	}
+	if c.Op == ONIL {
+		return
+	}
+	if c.Op != OLITERAL {
+		Fatalf("litsym c op %v", c.Op)
+	}
 	s := n.Sym.Linksym()
 	switch u := c.Val().U.(type) {
 	case bool:
diff --git a/src/cmd/compile/internal/gc/order.go b/src/cmd/compile/internal/gc/order.go
index 863de5b6c7..11c8b1fa25 100644
--- a/src/cmd/compile/internal/gc/order.go
+++ b/src/cmd/compile/internal/gc/order.go
@@ -119,7 +119,7 @@ func (o *Order) cheapExpr(n *Node) *Node {
 	}
 
 	switch n.Op {
-	case ONAME, OLITERAL:
+	case ONAME, OLITERAL, ONIL:
 		return n
 	case OLEN, OCAP:
 		l := o.cheapExpr(n.Left)
@@ -143,7 +143,7 @@ func (o *Order) cheapExpr(n *Node) *Node {
 // The intended use is to apply to x when rewriting x += y into x = x + y.
 func (o *Order) safeExpr(n *Node) *Node {
 	switch n.Op {
-	case ONAME, OLITERAL:
+	case ONAME, OLITERAL, ONIL:
 		return n
 
 	case ODOT, OLEN, OCAP:
@@ -202,7 +202,7 @@ func isaddrokay(n *Node) bool {
 // The result of addrTemp MUST be assigned back to n, e.g.
 // 	n.Left = o.addrTemp(n.Left)
 func (o *Order) addrTemp(n *Node) *Node {
-	if consttype(n) != CTxxx {
+	if n.Op == OLITERAL || n.Op == ONIL {
 		// TODO: expand this to all static composite literal nodes?
 		n = defaultlit(n, nil)
 		dowidth(n.Type)
diff --git a/src/cmd/compile/internal/gc/sinit.go b/src/cmd/compile/internal/gc/sinit.go
index 212fcc022d..c199ff6317 100644
--- a/src/cmd/compile/internal/gc/sinit.go
+++ b/src/cmd/compile/internal/gc/sinit.go
@@ -104,6 +104,9 @@ func (s *InitSchedule) staticcopy(l *Node, r *Node) bool {
 		s.append(nod(OAS, l, conv(r, l.Type)))
 		return true
 
+	case ONIL:
+		return true
+
 	case OLITERAL:
 		if isZero(r) {
 			return true
@@ -139,7 +142,7 @@ func (s *InitSchedule) staticcopy(l *Node, r *Node) bool {
 			e := &p.E[i]
 			n.Xoffset = l.Xoffset + e.Xoffset
 			n.Type = e.Expr.Type
-			if e.Expr.Op == OLITERAL {
+			if e.Expr.Op == OLITERAL || e.Expr.Op == ONIL {
 				litsym(n, e.Expr, int(n.Type.Width))
 				continue
 			}
@@ -171,6 +174,9 @@ func (s *InitSchedule) staticassign(l *Node, r *Node) bool {
 	case ONAME:
 		return s.staticcopy(l, r)
 
+	case ONIL:
+		return true
+
 	case OLITERAL:
 		if isZero(r) {
 			return true
@@ -232,7 +238,7 @@ func (s *InitSchedule) staticassign(l *Node, r *Node) bool {
 			e := &p.E[i]
 			n.Xoffset = l.Xoffset + e.Xoffset
 			n.Type = e.Expr.Type
-			if e.Expr.Op == OLITERAL {
+			if e.Expr.Op == OLITERAL || e.Expr.Op == ONIL {
 				litsym(n, e.Expr, int(n.Type.Width))
 				continue
 			}
@@ -269,13 +275,14 @@ func (s *InitSchedule) staticassign(l *Node, r *Node) bool {
 		for val.Op == OCONVIFACE {
 			val = val.Left
 		}
+
 		if val.Type.IsInterface() {
 			// val is an interface type.
 			// If val is nil, we can statically initialize l;
 			// both words are zero and so there no work to do, so report success.
 			// If val is non-nil, we have no concrete type to record,
 			// and we won't be able to statically initialize its value, so report failure.
-			return Isconst(val, CTNIL)
+			return val.Op == ONIL
 		}
 
 		markTypeUsedInInterface(val.Type, l.Sym.Linksym())
@@ -296,7 +303,7 @@ func (s *InitSchedule) staticassign(l *Node, r *Node) bool {
 
 		// Emit data.
 		if isdirectiface(val.Type) {
-			if Isconst(val, CTNIL) {
+			if val.Op == ONIL {
 				// Nil is zero, nothing to do.
 				return true
 			}
@@ -462,7 +469,7 @@ func isStaticCompositeLiteral(n *Node) bool {
 			}
 		}
 		return true
-	case OLITERAL:
+	case OLITERAL, ONIL:
 		return true
 	case OCONVIFACE:
 		// See staticassign's OCONVIFACE case for comments.
@@ -471,9 +478,9 @@ func isStaticCompositeLiteral(n *Node) bool {
 			val = val.Left
 		}
 		if val.Type.IsInterface() {
-			return Isconst(val, CTNIL)
+			return val.Op == ONIL
 		}
-		if isdirectiface(val.Type) && Isconst(val, CTNIL) {
+		if isdirectiface(val.Type) && val.Op == ONIL {
 			return true
 		}
 		return isStaticCompositeLiteral(val)
@@ -1105,13 +1112,14 @@ func (s *InitSchedule) addvalue(p *InitPlan, xoffset int64, n *Node) {
 
 func isZero(n *Node) bool {
 	switch n.Op {
+	case ONIL:
+		return true
+
 	case OLITERAL:
 		switch u := n.Val().U.(type) {
 		default:
 			Dump("unexpected literal", n)
 			Fatalf("isZero")
-		case *NilVal:
-			return true
 		case string:
 			return u == ""
 		case bool:
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 0b38e70cd2..709b2d434e 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -1993,7 +1993,7 @@ func (s *state) ssaShiftOp(op Op, t *types.Type, u *types.Type) ssa.Op {
 
 // expr converts the expression n to ssa, adds it to s and returns the ssa result.
 func (s *state) expr(n *Node) *ssa.Value {
-	if !(n.Op == ONAME || n.Op == OLITERAL && n.Sym != nil) {
+	if hasUniquePos(n) {
 		// ONAMEs and named OLITERALs have the line number
 		// of the decl, not the use. See issue 14742.
 		s.pushLine(n.Pos)
@@ -2029,6 +2029,16 @@ func (s *state) expr(n *Node) *ssa.Value {
 	case OCLOSUREVAR:
 		addr := s.addr(n)
 		return s.load(n.Type, addr)
+	case ONIL:
+		t := n.Type
+		switch {
+		case t.IsSlice():
+			return s.constSlice(t)
+		case t.IsInterface():
+			return s.constInterface(t)
+		default:
+			return s.constNil(t)
+		}
 	case OLITERAL:
 		switch u := n.Val().U.(type) {
 		case *Mpint:
@@ -2053,16 +2063,6 @@ func (s *state) expr(n *Node) *ssa.Value {
 			return s.entryNewValue0A(ssa.OpConstString, n.Type, u)
 		case bool:
 			return s.constBool(u)
-		case *NilVal:
-			t := n.Type
-			switch {
-			case t.IsSlice():
-				return s.constSlice(t)
-			case t.IsInterface():
-				return s.constInterface(t)
-			default:
-				return s.constNil(t)
-			}
 		case *Mpflt:
 			switch n.Type.Size() {
 			case 4:
diff --git a/src/cmd/compile/internal/gc/subr.go b/src/cmd/compile/internal/gc/subr.go
index 849043bfe2..7c13aef214 100644
--- a/src/cmd/compile/internal/gc/subr.go
+++ b/src/cmd/compile/internal/gc/subr.go
@@ -41,7 +41,7 @@ func hasUniquePos(n *Node) bool {
 	switch n.Op {
 	case ONAME, OPACK:
 		return false
-	case OLITERAL, OTYPE:
+	case OLITERAL, ONIL, OTYPE:
 		if n.Sym != nil {
 			return false
 		}
@@ -257,7 +257,9 @@ func nodintconst(v int64) *Node {
 }
 
 func nodnil() *Node {
-	return nodlit(Val{new(NilVal)})
+	n := nod(ONIL, nil, nil)
+	n.Type = types.Types[TNIL]
+	return n
 }
 
 func nodbool(b bool) *Node {
@@ -298,7 +300,7 @@ func treecopy(n *Node, pos src.XPos) *Node {
 		// crashing (golang.org/issue/11361).
 		fallthrough
 
-	case ONAME, ONONAME, OLITERAL, OTYPE:
+	case ONAME, ONONAME, OLITERAL, ONIL, OTYPE:
 		return n
 
 	}
@@ -308,7 +310,7 @@ func treecopy(n *Node, pos src.XPos) *Node {
 func (n *Node) isNil() bool {
 	// Check n.Orig because constant propagation may produce typed nil constants,
 	// which don't exist in the Go spec.
-	return Isconst(n.Orig, CTNIL)
+	return n.Orig.Op == ONIL
 }
 
 func isptrto(t *types.Type, et types.EType) bool {
@@ -807,7 +809,7 @@ func calcHasCall(n *Node) bool {
 	}
 
 	switch n.Op {
-	case OLITERAL, ONAME, OTYPE:
+	case OLITERAL, ONIL, ONAME, OTYPE:
 		if n.HasCall() {
 			Fatalf("OLITERAL/ONAME/OTYPE should never have calls: %+v", n)
 		}
@@ -926,7 +928,7 @@ func safeexpr(n *Node, init *Nodes) *Node {
 	}
 
 	switch n.Op {
-	case ONAME, OLITERAL:
+	case ONAME, OLITERAL, ONIL:
 		return n
 
 	case ODOT, OLEN, OCAP:
@@ -988,7 +990,7 @@ func copyexpr(n *Node, t *types.Type, init *Nodes) *Node {
 // result may not be assignable.
 func cheapexpr(n *Node, init *Nodes) *Node {
 	switch n.Op {
-	case ONAME, OLITERAL:
+	case ONAME, OLITERAL, ONIL:
 		return n
 	}
 
diff --git a/src/cmd/compile/internal/gc/swt.go b/src/cmd/compile/internal/gc/swt.go
index 9ab5f0c248..5f4e9e4b40 100644
--- a/src/cmd/compile/internal/gc/swt.go
+++ b/src/cmd/compile/internal/gc/swt.go
@@ -261,7 +261,7 @@ func walkExprSwitch(sw *Node) {
 	}
 
 	cond = walkexpr(cond, &sw.Ninit)
-	if cond.Op != OLITERAL {
+	if cond.Op != OLITERAL && cond.Op != ONIL {
 		cond = copyexpr(cond, cond.Type, &sw.Nbody)
 	}
 
diff --git a/src/cmd/compile/internal/gc/syntax.go b/src/cmd/compile/internal/gc/syntax.go
index b86510a294..f364ed1527 100644
--- a/src/cmd/compile/internal/gc/syntax.go
+++ b/src/cmd/compile/internal/gc/syntax.go
@@ -294,7 +294,7 @@ func (n *Node) SetIota(x int64) {
 // Extra care must be taken when mutating such a node.
 func (n *Node) mayBeShared() bool {
 	switch n.Op {
-	case ONAME, OLITERAL, OTYPE:
+	case ONAME, OLITERAL, ONIL, OTYPE:
 		return true
 	}
 	return false
diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index f13d9a3e26..32619b08d1 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -363,7 +363,7 @@ func typecheck1(n *Node, top int) (res *Node) {
 			n.Type = types.UntypedString
 		}
 
-	case ONONAME:
+	case ONIL, ONONAME:
 		ok |= ctxExpr
 
 	case ONAME:
@@ -1590,7 +1590,7 @@ func typecheck1(n *Node, top int) (res *Node) {
 
 		n.Type = t
 		if !t.IsSlice() {
-			if Isconst(args.First(), CTNIL) {
+			if args.First().isNil() {
 				yyerror("first argument to append must be typed slice; have untyped nil")
 				n.Type = nil
 				return n
@@ -3193,6 +3193,9 @@ func samesafeexpr(l *Node, r *Node) bool {
 
 	case OLITERAL:
 		return eqval(l.Val(), r.Val())
+
+	case ONIL:
+		return true
 	}
 
 	return false
@@ -3596,7 +3599,7 @@ func typecheckdef(n *Node) {
 		}
 		if !e.isGoConst() {
 			if !e.Diag() {
-				if Isconst(e, CTNIL) {
+				if e.Op == ONIL {
 					yyerrorl(n.Pos, "const initializer cannot be nil")
 				} else {
 					yyerrorl(n.Pos, "const initializer %v is not a constant", e)
diff --git a/src/cmd/compile/internal/gc/universe.go b/src/cmd/compile/internal/gc/universe.go
index 559d47da1a..32bf37e322 100644
--- a/src/cmd/compile/internal/gc/universe.go
+++ b/src/cmd/compile/internal/gc/universe.go
@@ -157,9 +157,7 @@ func lexinit() {
 
 	types.Types[TNIL] = types.New(TNIL)
 	s = builtinpkg.Lookup("nil")
-	var v Val
-	v.U = new(NilVal)
-	s.Def = asTypesNode(nodlit(v))
+	s.Def = asTypesNode(nodnil())
 	asNode(s.Def).Sym = s
 	asNode(s.Def).Name = new(Name)
 
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index a61cb3f651..ac43a8e1be 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -465,7 +465,7 @@ opswitch:
 
 	case ONONAME, OEMPTY, OGETG, ONEWOBJ:
 
-	case OTYPE, ONAME, OLITERAL:
+	case OTYPE, ONAME, OLITERAL, ONIL:
 		// TODO(mdempsky): Just return n; see discussion on CL 38655.
 		// Perhaps refactor to use Node.mayBeShared for these instead.
 		// If these return early, make sure to still call
@@ -2277,7 +2277,7 @@ func varexpr(n *Node) bool {
 	}
 
 	switch n.Op {
-	case OLITERAL:
+	case OLITERAL, ONIL:
 		return true
 
 	case ONAME:
@@ -2332,7 +2332,7 @@ func vmatch2(l *Node, r *Node) bool {
 	case ONAME:
 		return l == r
 
-	case OLITERAL:
+	case OLITERAL, ONIL:
 		return false
 	}
 
@@ -2373,7 +2373,7 @@ func vmatch1(l *Node, r *Node) bool {
 
 		return vmatch2(l, r)
 
-	case OLITERAL:
+	case OLITERAL, ONIL:
 		return false
 	}
 
@@ -3190,7 +3190,7 @@ func eqfor(t *types.Type) (n *Node, needsize bool) {
 // The result of walkcompare MUST be assigned back to n, e.g.
 // 	n.Left = walkcompare(n.Left, init)
 func walkcompare(n *Node, init *Nodes) *Node {
-	if n.Left.Type.IsInterface() && n.Right.Type.IsInterface() && n.Left.Op != OLITERAL && n.Right.Op != OLITERAL {
+	if n.Left.Type.IsInterface() && n.Right.Type.IsInterface() && n.Left.Op != ONIL && n.Right.Op != ONIL {
 		return walkcompareInterface(n, init)
 	}
 
@@ -3788,6 +3788,7 @@ func candiscard(n *Node) bool {
 		OTYPE,
 		OPACK,
 		OLITERAL,
+		ONIL,
 		OADD,
 		OSUB,
 		OOR,
diff --git a/src/cmd/compile/internal/types/type.go b/src/cmd/compile/internal/types/type.go
index 62c5c34484..82db9e4dbc 100644
--- a/src/cmd/compile/internal/types/type.go
+++ b/src/cmd/compile/internal/types/type.go
@@ -1265,7 +1265,7 @@ func (t *Type) IsPtrShaped() bool {
 // HasNil reports whether the set of values determined by t includes nil.
 func (t *Type) HasNil() bool {
 	switch t.Etype {
-	case TCHAN, TFUNC, TINTER, TMAP, TPTR, TSLICE, TUNSAFEPTR:
+	case TCHAN, TFUNC, TINTER, TMAP, TNIL, TPTR, TSLICE, TUNSAFEPTR:
 		return true
 	}
 	return false